Invented by Willie Berg in 1935 the Humes & Berg Stonelined mute features a secret formula used in the lining for easy blowing and perfect intonation. Willie Berg invented Stonelined Mutes in 1935. They are among the finest brass instrument mutes available in the world. Stonelined Mutes deliver the perfect professional sound all the time. Included in the many Stonelined Mute features that allow the outstanding colors of sound is the secret formula used to line each and every Stonelined Mute.